Silicon materials are known to be used as a constituent of a semiconductor, a solar battery, a secondary battery or the like, and studies on silicon materials are actively conducted in recent years.
For example, Non-Patent Literature 1 describes synthesizing layered polysilane by reacting CaSi2 with acid.
Patent Literature describes synthesizing layered polysilane by reacting CaSi2 with acid, and describes that a lithium ion secondary battery having the layered polysilane as an active material exhibits a suitable capacitance.
Patent Literature 2 describes synthesizing a layered silicon compound of which main component is layered polysilane in which Ca is removed by reacting CaSi2 with acid, and heating the layered silicon compound at not less than 300° C. to produce a silicon material from which hydrogen is removed, and also describes that a lithium ion secondary battery having the silicon material as an active material exhibits a suitable capacity retention rate.
In CaSi2, impurities such as crystalline silicon, Ca14Si19, and the like occasionally exist. Non-Patent Literature 2 describes subjecting CaSi2 that contains impurities to a heating treatment at high temperature so as to convert the impurities into CaSi2.